New init system

[edubart]

This PR implements:

• 70

• 93

This PR also fixes:

• https://github.com/cartesi/machine-emulator-tools/issues/6
• https://github.com/cartesi/machine-emulator-tools/issues/9
• https://github.com/cartesi/machine-emulator-tools/issues/10

This PR requires a new kernel, new init script and new rootfs.

Depends on

• https://github.com/cartesi/grpc-interfaces/pull/18
• https://github.com/cartesi/image-kernel/pull/32
• https://github.com/cartesi/machine-emulator-tools/pull/16